The wikipedia article on the PMI says

When we develop a new theory, the central ideas of the old one usually become refuted. Parts of the old theory, however, we carry over to the new one

This seems to be at least part of the reason we have alternatives to "naive realism".

But there's no agreement on what parts of our current theories are knowledge and should be retained.

Can't philosophers identify a commonality between what actually has been retained through past theory change? And if there is no commonality, what then?

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    There is indeed no agreement among (traditional) scientific realists on how to respond to pessimistic induction, this is why the favored form of realism currently is structural realism, "scientific theories tell us only about the form or structure of the unobservable world and not about its nature", mathematical structure that is. Abandoned theories are usually "degenerate limits" in some sense of the ones replacing them (Bohr's "correspondence principle"), so some mathematical "commonality" can always be found. – Conifold Feb 17 '17 at 23:23
  • @Conifold any idea what could be "unclear" about this question? – user6917 Feb 18 '17 at 16:46
  • And what part of the theory of epicycles was carried over into the Sun centric theory of Copernicus? – Swami Vishwananda Feb 20 '17 at 7:57
  • Not sure, maybe pessimistic induction (especially abbreviated as PMI) is not that well-known, so the context of the questions at the bottom did not come through for some people. @SwamiVishwananda Epicycles are just a geometric form of writing Fourier series. When modern formulas expressed in geocentric frame are expanded into a series the leading coefficients will be close to Ptolemy's values (by the way, Copernicus kept epicycles, only Kepler eliminated them by replacing circles with ellipses). See Hanson's Mathematics of Epicycles. – Conifold Feb 20 '17 at 18:48

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